Turbine Valve Research Articles

Research and application of self-diagnosis and automatic intervention functions for turbine regulating valve malfunctions in nuclear power plants

Abstract The inlet regulating valve of the turbine is very important to the control of the turbine. If the control is abnormal, it will create some uncontrollable safety risks, which may cause the turbine to trip, even to over-speed. The study of the structure and control mode of the turbine regulating valve shows some defects in the design of the turbine regulating valve in a nuclear power plant. In this paper, through the analysis of the fault mode, the method of fault self-diagnosis is studied, verified, and improved so that it has perfect self-diagnosis and intervention means, improves the reliability of turbine valve control, and eliminates the hidden danger of tripping.

Numerical studies of sCO2 Brayton cycle

This work describes the one-dimensional, thermo-hydraulic model of the sCO2 cycle Sofia developed to investigate optimal control methods and the behaviour of the cycle during operation. This dynamic model includes all devices such as turbomachinery, heat exchangers, valves, and piping including heat loss, in line with concept of the 1 MWe sCO2 cycle, to be realised in the site of a fossil power plant in the Czech Republic.The model assembly and calculations were conducted using the commercial Modelica-based library ClaRa + using the simulation environment Dymola and in combination with another Modelica-based library, UserInteraction; the real-time simulations, with some parameter changes during the calculation, are made and described in this paper.Nominal parameters were achieved during the steady-state simulation, except for the lower mass flow of sCO2. Transient simulation of power turbine start-up from standby state and results are also presented in this paper. The nominal state is achieved with the semi-automatic procedure in approx. 3 h. The simulation results allow more detailed analyses of control methods and a better understanding of real device control and behaviour during start-up, shutdown, or other transients.Careful manipulation of turbine valves in coordination with the pressuriser operation was identified as crucial for optimal control of the system. Also, the initial amount of CO2 in the pressuriser affects its behaviour during transients.

Health assessment of an electro-hydraulic servo pump control system for servomotor based on LGA deep neural network

Due to its advantages of having a high power-to-weight ratio and being energy-efficient, the electro-hydraulic servo pump control system (abbreviated as EHSPCS) is frequently employed in the industrial field, such as the electro-hydraulic servo pump control (EHSPC) servomotor for steam turbine valve regulation control. However, the EHSPCS has strong nonlinearity and time-varying features, and the factors that cause system performance degradation are complex. Once a system failure occurs, it may lead to serious accidents, causing serious casualties and economic losses. To address the above issues, a system health assessment method based on LSTM-GRNN-ANN (LGA) deep neural network is proposed in this paper. Firstly, with oil volume gas content, servo motor air-gap flux density, and system leakage coefficient as the health assessment performance indicators, a health assessment performance index system for the EHSPCS is built, Furthermore, the system performance index threshold is set. Secondly, an LGA deep neural network is constructed by combining LSTM, GRNN and ANN, and a deep neural network based on the LGA is used to create an EHSPCS health assessment model. Subsequently, system feature parameter extraction, algorithm design, and parameter debugging are carried out. Finally, an EHSPCS experimental platform is established, typical system failure simulation experiments are designed, and comparative experimental analysis is conducted. The experimental findings demonstrate that the average accuracy of the system health assessment model based on the LGA deep neural network suggested in this paper is 96.37%, compared to 89.84%, 87.99% for LSTM and GRNN, which validates the accuracy of the system health assessment model based on the LGA deep neural network.

A Combined Delayed Detached Eddy Simulation and Linearized Navier–Stokes Equation Study on the Generation and Reduction of Aerodynamic Noises Inside Steam Turbine Control Valve With Acoustic Liner

Abstract This study was aimed at numerically investigating the source, generation mechanism, and strategy for reducing aerodynamic noises inside a steam turbine control valve. A delayed detached eddy simulation was performed to extract the three-dimensional unsteady turbulent flow structures formed within the serpentine flow passage of the turbine valve. Acoustic analogies, spatial Fourier transform, and spectral proper orthogonal decomposition on the delayed detached eddy simulation-simulated flow data were complementarily combined to clarify the generation mechanism of tonal and broadband aerodynamic noises. The results showed that broadband noises were produced by wall-attached jet flow and turbulent mixing flow between the annular wall jets and central reverse flow. High-intensity tonal noises were generated by the excitation of multi-order natural acoustic modes of the bell-shaped valve spindle. The intensive acoustic pressure pulsations concentrated inside the bell jar and propagated along the diffuser to the downstream turbine chamber. A novel ring acoustic liner was designed using the acoustic impedance model to reduce the valve noises without sacrificing the flow performance. The noise reduction effectiveness was evaluated by solving the linearized Navier–Stokes equations in the frequency domain.

Research on the flow characteristics identification of steam turbine valve based on FCM-LSSVM

Due to aging and deformation of the through-flow path and system modifications, the flow characteristics of the turbine inlet valve often deviate from the design value, which affects the unit load control accuracy and operational stability. In order to obtain the actual valve flow characteristics of the turbine and thus improve the FM performance, an FCMLSSVM model is proposed in this paper to identify the valve flow characteristics. First, FCM clustering is proposed to classify the historical operating data of the plant and obtain a wide range of variable operating conditions. Then, using least squares support vector machine (LSSVM), the relationship between turbine input and output variables was modeled in each condition cluster, with integrated valve position command, speed, and real power generated as input variables and actual steam inlet flow as output variables. Using a 330 MW turbine unit as an application example, the established FCM-LSSVM model was validated for the valve flow characteristics of the turbine. The results show that the model can obtain accurate valve flow characteristics without conducting tests on the turbine. The method can save a lot of labor and material resources in doing the characteristic test, and after comparison, the proposed method can identify the flow characteristics more accurately among the existing neural network identification methods, which can provide technical support to improve the unit frequency regulation characteristics and improve the accuracy of valve operation.

Study on the sealing test method of hydraulic solenoid valve in nuclear power station

In order to improve the reliability of tripping solenoid valve and switching solenoid valve of steam turbine valve in nuclear power plant and reduce abnormal valve closing. According to the working principle of valves in nuclear power plant, this paper designs a kind of electromagnetic valve sealing test system, including test base, measurement and control system and hydraulic system. The detection system is an offline system. By simulating the real load condition of the steam turbine system, the tightness of the tripping solenoid valve and the switching solenoid valve is tested to improve the reliability of the solenoid valve. The actual application results show that the system operates stably and reliably, is simple to operate, has high detection efficiency and accuracy, and has good use effect.

Numerical Simulation of Temperature Field in Ultra-Narrow Arc Welding of Thick-Walled Steam Turbine Valve Body Material

The welding problems of large and thick plates are becoming more prominent as the application of large-scale and thick-plate metal structures grows. Due to the issue of excessive welding deformation between the 60mm thick steam turbine valve body and the pipe joint, a new process method is employed to connect. In this paper, the welding technology of flux strip confined arc ultra-narrow gap is proposed to carry out welding test on the ZG13Cr9Mo2Co1NiVNbNB cast steel test block of steam turbine valve body material with a thickness of 60 mm. The welding temperature field is measured by means of a K-type thermocouple and numerical simulation. The results show that the thermal cycle curve obtained by the homogeneous body heat source simulation is basically consistent with the thermal cycle curve measured during the experiment, and the simulation results of the molten pool morphology are also consistent with the actual macroscopic morphology of the weld.

Economic dispatch using modified bat algorithm

Due to the frequent opening and shutting of turbine valves in the power system, valve point effect (VPE) that makes the economic dispatching (ED) problem non-linear, non-smooth and non-convex may be generated. Moreover, various constraints appear in the operation process, such as network transmission loss, and power balance during unit operation, which make it more difficult to find the global optimum through traditional mathematical methods. Nowadays, intelligent algorithms have successfully become a useful optimization tool to deal with nonlinear problems. In this paper, an improved bat algorithm (IBA), into which random black hole strategy and Gaussian mutation are introduced, is proposed to solve the ED problem. Furthermore, the random black hole strategy can enhance the diversity of the population and improve the convergence speed of IBA. Gaussian mutation is adopted to help jumping out of the local optimum. IBA is tested in 50 and 100 dimensions on 10 sets of well-known benchmark functions respectively, and compared with the methods in literature to verify its feasibility. Then, three different scales economic dispatching problems (3 units, 13 units, 40 units) are solved by this method, which further proves its effectiveness. The results show that IBA has obvious advantages and practical application value compared with other optimization methods.

Reserve replacement from governor to energy storage system on conventional generator for operating-cost reduction

This paper proposes an operation strategy for a steam turbine generator (GEN) with a built-in energy storage system (ESS) that replaces the role of the governor. The proposed strategy cuts the operating cost of GEN by minimizing the throttling loss and the amount of fuel with the harmonious operation of ESS. For the conventional governor droop control, the valve cannot be fully open for emergency release; it causes losses in the throttle valve and fuel cost due to the reserve. Beyond these limitations, in the proposed coordinated operation between GEN and ESS, the GEN can operate in the natural sliding pressure mode, which fully opens the steam turbine valves, reduces the steam pressure, and improves the efficiency of the turbine by minimizing the throttling loss. In this method, while a generator produces constant power without the reserve for an emergency condition in the proposed coordinated operation, an ESS is in charge of fast primary frequency control. Subsequently, the GEN can achieve a replaced reserve operation by ESS, which removes the constant operational loss by reserved steam and provides economic advantages by reducing operation costs. We theoretically demonstrate that the proposed operation provides a quick and reliable frequency control performance through frequency- and time-domain analysis compared with the conventional operation. Using a power generation simulator practically installed at Korea Western Power Co., Ltd., we also proved that the proposed operation can yield the economic benefit based on the cost reduction by minimizing losses of GEN, and provide an improved frequency regulation performance with the coordinating operation.

DEVELOPMENT OF NONLINEAR MODEL OF NPP STEAM GENERATOR FOR INFORMATION TECHNOLOGY OF CONTROL OPTIMIZATION

Steam generators of modern power units of nuclear power plants are critical elements of power units and are subject to modernization. Identification of the steam generator model for optimizing the control of the steam generator is an urgent task. The purpose of this article is to develop a nonlinear mathematical model of a steam generator in relative variables for its use in information technology for optimizing control. Mathematical models of heat transfer and steam formation processes in a steam generator are presented in the form of systems of differential equations in relative variables. These models are intended for simulation modeling of thermal processes in a steam generator. Thermal processes are associated with the supply of feed water to the steam generator from the water treatment system and coolant from the nuclear reactor, as well as with the removal of steam from the steam generator to the main steam collector. According to the law of conservation of the momentum of the working medium in the circulation circuit of the steam generator under the evaporation mirror, a nonlinear differential equation for the process of circulation of the steam-water mixture is obtained. A nonlinear differential equation has been developed to calculate the derivative of the steam flow through the evaporation mirror in relative variables. The equations for the auxiliary equipment – the main steam header, the steam turbine valve actuator and the control feed valve actuator – are reduced to relative variables. Using the equations of heat transfer, steam formation, circulation and auxiliary equipment, a nonlinear model of the steam generator in the state space as a control object in relative variables is constructed. Formulas are given for calculating the values of the constant parameters of the steam generator model from the values of its design and technological parameters. A program for a nonlinear mathematical model of the PGV-1000 steam generator has been developed, which is included in the information technology steam generator model module. This will make it possible to solve the problems of identifying and optimizing the information control system of the water level in the steam generator PGV-1000 of the power unit with a nuclear reactor VVER-1000.

Profit based unit commitment problem solution using metaheuristic optimisation approach

Earlier power utilities had generated electrical power with the goal of minimising the costs and meeting both demand and reserves. Generation companies (GENCOs) schedule their generators under a new structure to maximise the profit. This paper provides a computational methodology based on monarch butterfly optimisation (MBO) to find a solution to the problem of profit-based unit commitment (PBUC), taking into account the power and reserve conditions. The proposed method allows GENCOs to determine how much power and reserve should be sold in the markets in order to achieve maximum profit. The binary variables of unit commitment problems are handled by modifying the continuous-time nature of the monarch butterfly algorithm. The computational approach maximises the profit but also handles the mixed constraints of the commitment problem. The effect of thermal turbine valve point loading is also taken into consideration. The computational technique has been used to solve two test systems in the absence and presence of steam turbine valve point loading effects. The results obtained are in agreement with the recent results available in the literature. Comparative analysis shows the effectiveness of the proposed MBO based solution methodology in terms of profit earned and execution time in relation to other techniques.

Strength and Service Life of a Steam Turbine Stop and Control Valve Body

The stability of operation of steam turbines depends (along with other factors) on the reliable operation of their steam distribution systems, which are based on stop and control valves. This paper considers the strength of the elements of the K-325-23.5 steam turbine valves, in whose bodies, after 30 thousand hours of operation, cracks came to be observed. Previously determined were the nature of gas-dynamic processes in the flow paths of the valves and the temperature state of the valve body in the main stationary modes of operation. To do this, a combined problem of steam flow and thermal conductivity in stop and control valves was solved in a three-dimensional formulation by the finite element method. Different positions of the valve elements were considered taking into account the filter sieve. The assessment of the thermal stress state of the valve body showed that the maximum stresses in different operating modes do not exceed the yield strength. Therefore, the assessment of the creep of the valve body material is important to determine the valve body damage and service life. Modeling the creep of the stop and control valves of the turbine was performed on the basis of three-dimensional models, using the theory of hardening, with the components of unstable and steady creep strains taken into account. The creep was determined at the maximum power of the turbine for all the stationary operating modes. The maximum calculated values of creep strains are concentrated in the valve body branch pipes before the control valves and in the steam inlet chamber, where in practice fatigue defects are observed. However, even for 300 thousand hours of operation of the turbine (with a conditional maximum power) in stationary modes, creep strains do not exceed admissible values. The damage and service life of the valve bodies were assessed by two methods developed at A. Pidhornyi Institute of Mechanical Engineering Problems of the NAS of Ukraine (2011), and I. Polzunov Scientific and Design Association on Research and Design of Power Equipment. (NPO CKTI) – 1986. The results of assessing the damage and the turbine valve body wear from the effects of cyclic loading and creep of the turbine in stationary modes for 40, 200 and 300 thousand hours show that the thermal conditions of the body in the steam inlet chamber are not violated (without taking into account possible body defects after manufacture). The damage in valve body branch pipes after 300 thousand hours of operation exceeds the admissible value, with account taken of the safety margin. At the same time, the damage from creep in stationary operating modes is about 70% of the total damage. The maximum values of damage are observed in the areas of the body where there are defects during the operation of the turbine steam distribution system. The difference between the results of both methods in relation to their average value is ~20%.

Analysis and Treatment of the Failure of Speed Closing Valve of Small Steam Turbine of Boiler Feed Pump of 660MW Supercritical Unit

Analysis and Treatment of the Failure of Speed Closing Valve of Small Steam Turbine of Boiler Feed Pump of 660MW Supercritical Unit

Analysis of dynamic characteristics and influencing factors of steam dump conditions of marine nuclear power plant

Objectives Based on the operation requirements of steam bypass exhaust system of marine nuclear power plant, the dynamic characteristics and influencing factors of bypass exhaust conditions are analyzed. Methods According to the functional characteristics of the steam bypass exhaust system, the mathematical and physical models of the matching operation of the steam generator, steam system, bypass system and main steam turbine are established. The dynamic operation characteristics and the coupling matching characteristics of the primary and secondary circuits under extreme working conditions such as quick closing of the main steam valve and load rejection of the steam turbine are analyzed to verify the accuracy and universality of the simulation model. Results The simulation results show that when operating under bypass exhaust condition, the appropriate bypass exhaust valve, main steam valve and their matching action time should be selected according to the power self-regulation capacity of the marine reactor, and the safety problems such as overpressure of the steam header and overspeed of the steam turbine unit should be comprehensively considered. At the same time, the steam demand of other equipments on the ship should be met. Conclusions The research results can provide reference for the safety control of side exhaust conditions and the optimal design of side exhaust system of nuclear power plant.

On-Line Control of Stresses in the Power Unit Pressure Elements Taking Account of Variable Heat Transfer Conditions

Coal-fired power units, now balancing power shortages in the power system, must be characterised by increasingly higher flexibility of operation. This means faster start-ups and the capacity for frequent decreases and increases in the power output. These processes cause large temperature gradients in elements of the power unit and the turbine and lead to an increase in the stress level. At such an operating regime it is impossible to ensure safety based on start-up characteristics only—it becomes necessary to constantly monitor stress levels in critical areas of machinery and equipment elements. The stress level in turbine elements can be monitored on-line using algorithms based on Green’s functions and Duhamel’s integral. This paper presents examples of modifications of stress calculations in turbine valves and casings during start-ups. By modifying basic algorithms, it is possible to take into account the impact of the variability of heat transfer coefficients on the thermal stress level. Additionally, individual Green’s functions and correction factors were determined for specific stages of start-ups. Due to modifications, it is possible to obtain satisfactory agreement with the results obtained from FEM-based calculations for the entire heating process. Equations are also given that enable estimation of values of the heat transfer coefficient in turbine valves. The proposed modification of the algorithm will substantially improve the accuracy of stress modelling in transient states of the turbine operation. On-line stress monitoring will enable an increase in the flexibility of the power unit operation and facilitate operational control, ensuring safety of individual elements at the same time. The stress values calculated in the on-line mode can also be used to estimate fatigue life consumption and forecast the residual lifetime of individual components.

A Comprehensive Heat Transfer Study Inside a Steam Turbine Valve: Experiment, Numerical Simulation, and Simplified Model

Abstract In a steam turbine system, one of the main factors limiting the operational flexibility is the thermal stress associated with a high-temperature gradient within the control valves, which often leads to structural damage during frequent startup and shutdown cycles. One possible solution is to utilize an electric heating system with appropriate insulation to decrease the warm-up time. Here, an experiment and a numerical simulation were performed using a scaled turbine valve equipped with an electric heating system to understand the heat transfer process. The experiment, which was conducted at Shanghai Jiao Tong University, had a duration of 100 h and included three heating–cooling cycles and two heat preservation states. The results showed that the temperature distribution of the scaled valve was uniform, which is due to the high thermal conductivity of the valve body and the low conductivity of the insulation layer. The simulation, which used the commercial software ansysfluent 2019 R1, was performed to model the experimental heat transfer process and showed less than 10% deviation from the measured temperatures. A sensitivity study revealed that the valve temperature is very insensitive to the heat transfer coefficient of the outer surface of the insulation layer, which is attributed to the negative feedback regulation of radiation heat transfer. To further improve the computing efficiency, a simplified model based on the lumped parameter method and the quasi-steady-state assumption was proposed and validated. This model can predict the 100 h valve temperature history in less than 1 min and showed good agreement for all of the studied cases. The ability of the simplified model to simulate the valve heating–cooling cycles at a high efficiency could accelerate the thermal design process to improve the operational flexibility of steam turbines in the future.

Using MPC to Balance Intermittent Wind and Solar Power with Hydro Power in Microgrids

In a microgrid connected with both intermittent and dispatchable sources, intermittency caused by sources such as solar and wind power plants can be balanced by dispatching hydro power into the grid. Both intermittent generation and consumption are stochastic in nature, not known perfectly, and require future prediction. The stochastic generation and consumption will cause the grid frequency to drift away from a required range. To improve performance, operation should be optimized over some horizon, with the added problem that intermittent power varies randomly into the future. Optimal management of dynamic system over a future horizon with disturbances is often posed as a Model Predictive Control (MPC) problem. In this paper, we have employed an MPC scheme for generating a hydro-turbine valve signal for dispatching necessary hydro power to the intermittent grid and maintaining grid frequency. Parameter sensitivity analysis shows that grid frequency is mostly sensitive to the turbine valve signal. We have found that controller discretization time, grid frequency, and power injection into the grid are interrelated, and play an important role in maintaining the grid frequency within the thresholds. Results also indicate that the fluctuations in grid frequency are insignificant on the turbine valve position during power injection into the grid.

Validation of installation effects of an ultrasonic flow meter on butterfly valve using numerical analysis

Custody transfer in measurement of flow is referred as fiscal metering where the change of ownership involves. Metering errors in custody transfer calls for a rapid improvement in flow measurement technology. However, standard ideal and field real conditions vary due to the constraints such as non-availability of straight length at upstream and downstream piping, disturbances of flow elements of valves, bends etc will lead to variation in accuracy of flow meters do not permit to fulfill this requirement. Flow metering technique such as acoustic method is recommended as complement flow measuring technique for hydro turbines. The motivation of the study is drawn from a typical penstock of hydro plants where the straight lengths on penstocks are generally not available and the flow through the conductor system is regulated by valves. The flow distortion effect of flow elements causes the extent of errors during the flow metering. The numerical and experimental investigations are presented in this paper is to highlight the installation effects and simulate the variation in accuracy for flow rate measurement using clamp on type flow meter by inverse method at the main inlet valve of a hydro turbine. A commercial CFD Fluent solver is used to validate the velocity distortion of the installation on the closed conduit. The CFD analysis is useful for faster analysis on the installation effects where the limitation of time constraints. A reference can be drawn from the results where standard straight lengths are not met. These findings are also useful in selecting a suitable location for the installation of ultrasonic flow meters and helps in identifying the proper location for the installation flow disturbances like bends, valves and spool elements. The findings are useful in eliminating the uncertainty for the performance evaluation of hydro turbines where the flow is one of a vital parameter in improvement of system.

Pressure losses and oscillations in a compact valve of a steam turbine

Characteristics of a new compact valve design for steam turbines are analysed by measuring pressure losses and oscillations on the valve model. It is the model of an intercept valve of the intermediate-pressure turbine part. This valve is relatively smaller hence cheaper than usual control and intercept valves. Besides, four different valve seat angles were tested in order to investigate the valve seat angle influence. In order to further clarify measured phenomena, the wide range of numerical simulations were also carried out. Measurements were performed in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences in an air test rig installed in a modular aerodynamic tunnel. Numerical simulations were performed in the Doosan Skoda Power Company using a package of ANSYS software tools. Measurement results are compared with numerical and generalized in the form of valve characteristics and pressure oscillation maps. As a result of the pressure loss analysis, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern compact valves are used. As a result of the pressure oscillation analysis, operating conditions at which dangerous flow instabilities can occur were identified. Thanks to this, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

Integrated control of torque and emission of a diesel engine based on LPV‐MPC

This study presents an integrated control scheme of a diesel engine which aims to ensure quick torque response while limiting the average NOx emission below the certain specification. To start with, the sensitivity analysis is performed to recognize the key factors determined to balance emission, torque and fuel consumption. Considering the strong nonlinearity of the diesel engine, a multi-input multi-output (MIMO) linear parameter varying (LPV) model is developed. Unlike the conventional state-depended LPV modelling process, the proposed LPV model is built based on a kernel function with a novel form of state-free predictive equation so that the system outputs are directly computed. The control objective of coordinating torque tracking and emission reduction is then accomplished by designing a model predictive controller that regulates the fuel injection quantity, fuel injection angle, exhaust gas recirculation (EGR) rate and the opening degree of variable geometry turbine (VGT) valve. Finally, the developed LPV model and the MPC controller are testified with a high-fidelity commercial diesel engine model. The results show that the LPV-MPC controller is able to satisfy the NOx emission specification and the engine torque tracks the desired reference fast in transients, while the control variables are suitably actuated within the actuator constraints.